1. Field of the Invention
The present invention relates to a method for preventing copper and zinc from being eluted from a copper-alloy-made plumbing instrument including valves, pipe joints, water faucets and copper pipes, to a copper-alloy-made plumbing instrument using the method and to a film-forming agent.
2. Description of the Prior Art
Usually, copper alloy including bronze and brass is excellent in castability, machinability and economy and is generally used widely as a material for a plumbing instrument including valves and pipe joints for water service, water supply and hot-water supply, strainers, faucets and copper pipes because it exhibits a high antibacterial action other materials are difficult to exhibit.
Tap water is set to suit the water quality standard established by the Ministerial Ordinance on Water Quality Standard under Article 4 of Japan Water Works Law. The water quality standard of tap water includes substances set as an item on health and substances set as an item on properties tap water should have, and copper and zinc belong to the latter item.
Copper, an element, is indispensable to human beings, and it is held that the amount of copper necessary for adults is 2 mg/day. However, tap water containing copper in the amount of 1.0 mg/l or more takes on a metallic taste and such a level colors laundry and induces contamination in plumbing equipment. Therefore, the water quality standard sets that the amount of copper in water is less than 1.0 mg/l. Incidentally, though copper is an indispensable element, human beings having ingested copper over an allowable amount suffer from attack of fever, abdominal pains, bout of vomiting, big split, mouth dryness, breathing disorder, bluely coated tongue and cirrhosis and are possibly hemolyzed.
Zinc, an element, is also indispensable to human beings, and it is held that the amount of zinc necessary for adults is 15 to 22 mg/day. However, when tap water containing zinc in the amount of 1.0 mg/l or more has been brought to a boil, it is made cloudy to destroy tea flavor, and tap water containing zinc in the amount of 3.0 mg/l is made cloudy to induce white water. Furthermore, tap water containing zinc in the amount of 5.0 mg/l or more induces an astringent taste and, when having being placed in a bath, we have found a case where oil film float on the surface of the tap water. In view of these facts, the amount of zinc under the water quality standard is generally set to be 1.0 mg/l or less from the standpoints of taste sense and color. Incidentally, though zinc is an indispensable element, human beings having ingested zinc over an allowable amount possibly undergo the manifestation of toxicity including abdominal pains, big split and diarrhea.
For these reasons, in the Ministerial Ordinance on Water Quality Standard, for example, the water-supply equipment elution performance standards for individual copper-alloy-made plumbing instruments including valves, pipe joints, faucets and copper pipes have been established, and observing the water quality standards has aspired. Valves and pipe joints belong to the classification of water-supply implements or water-supply pipes other than the fringe of the water-supply equipment elution performance standards, in which the standard value of copper is 1.0 mg/l and that of zinc is 1.0 mg/l. Faucets belong to the classification of faucet and other fringe water-supply implements of the water-supply equipment elution performance standards, in which the standard value of copper is 0.1 mg/l and that of zinc is 0.1 mg/l as shown in the table of JIS B2061 water-supply faucets. In the single faucets and hot-water and water mixing faucets using copper alloy, the standard value of copper and that of zinc are set to be 0.98 mg/l, respectively, as the special case values.
In the meantime, it has been reported that in some of recent drinking water treatment plants using copper-alloy-made plumbing instruments, the concentration of copper in tap water exceeds 50% or more of the water quality standard. Since it is conceivable that the main sources of lixiviation thereof are valves, pipe joints and faucets made of copper alloy including bronze or brass made preponderantly of copper and zinc, further elution prevention countermeasures have been needed.
Methods for preventing elements contained in copper-alloy-made liquid-contact members from being eluted or protecting the surfaces of the members have been proposed in the following Patent Documents. The lead elution prevention method of Patent Document 1, for example is directed to removal of lead on the surface of a plumbing instrument through washing the surface with acid. The lead elution reduction treatment method of Patent Document 2 is directed to removal of lead of the surface through immersing lead-containing copper alloy in an alkaline etching solution having an oxidant added thereto. The nickel elution prevention method of Patent Document 3 comprises washing with acid nickel salt adhering to the surface layer of a liquid-contact portion of a plumbing instrument plated with nickel, removing the nickel salt by washing and forming a coat on the surface of the liquid-contact portion with hydrochloric acid to undergo a denickelification treatment. On the other hand, as a method for preventing the elution of harmful elements through coating the surface of copper alloy, a plating construction method has also been used. In this case, plating materials for coating the surface of copper alloy include NiCr coat, Ni coat, tin coat, silver coat, gold coat, platinum coat, rhodium coat, palladium coat, iridium coat and hard chrome.
Other related conventional techniques are proposed in Patent Documents 4 to 7. Patent Document 4 relates to a technique for preventing occurrence of verdigris, comprising immersing copper-alloy-made faucet equipment in an aqueous organic acid solution to selectively elute zinc and lead and form a film through bonding of the surface copper and the organic acid. Patent Document 5 relates to a technique of forming a lead elution prevention layer containing a substance having lead-selection complementation on the surface of copper alloy that is water-contact member and forming thereon a layer containing a water-repellent substance, wherein the water-repellent substance is silicone or fluorine resin. Furthermore, Patent Document 6 relates to a technique on surface treatment of chemically plating the surface of a copper molded article with an alloy film of antimony and nickel, and Patent Document 7 relates to a technique for suppressing elution of nickel, comprising applying protective film formation agent containing wax to the surface of a copper-alloy-made liquid-contact instrument treated with nickel plating.